Valve metal and valve metal oxide agglomerate powders and method for the production thereof

ABSTRACT

At least one of a valve metal sintered capacitor anode body and a suboxide valve metal sintered capacitor anode body with a particle density of &gt;88% of a theoretical density.

CROSS REFERENCE TO PRIOR APPLICATIONS

This application is a U.S National Phase application under 35 U.S.C.§371 of International Application No. PCT/EP2009/060912, filed on Aug.25, 2009 and which claims benefit to German Patent Application No. 102008 048 614.0, filed on Sep. 23, 2008. The International Applicationwas published in German on Apr. 1, 2010 as WO 2010/034577 A1 under PCTArticle 21(2).

FIELD

The present invention relates to valve metal and valve metal oxideagglomerate powders (valve metals are Nb, Ta, Ti, Zr, Hf, V, Mo, W, Al)and mixtures and alloys thereof, for example, of niobium and/or tantalumor niobium suboxide, for producing capacitors and sintered anode bodiesfor capacitors.

BACKGROUND

Solid electrolytic capacitors with a very large active capacitor area,which are therefore of a small design suitable for mobile communicationselectronics, are predominantly those with a niobium or tantalumpentoxide barrier layer applied to an appropriate conductive carrier,utilizing the stability of said barrier layer (“valve metal”), thecomparatively high dielectric constants and the insulating pentoxidelayer producible with a very homogeneous layer thickness by means of theelectrochemical generation method. The carriers used are metallic orconductive lower oxidic (suboxide) precursors of the correspondingpentoxides. The carrier, which simultaneously constitutes a capacitorelectrode (anode), consists of a highly porous, spongelike structurewhich is produced by sintering ultrafine primary structures or alreadyspongelike secondary structures. The surface of the support structure isoxidized electrolytically (“formed”) to the pentoxide, the thickness ofthe pentoxide layer being determined by the maximum voltage of theelectrolytic oxidation (“forming voltage”). The counterelectrode isobtained by impregnating the spongelike structure with manganesenitrate, which is converted thermally to manganese dioxide, or with aliquid precursor of a polymer electrolyte or of a polymer dispersion ofa conductive polymer and polymerizing, for example, PEDT. The electricalcontacts to the electrodes are produced on one side by a tantalum orniobium wire incorporated by sintering in the course of generation ofthe carrier structure and, on the other side, by the metallic capacitorshell insulated from the wire.

The capacitance C of a capacitor is calculated by the following formula:

C=(F·ε)/(d·V _(F))

where F denotes the capacitor surface area, ε the dielectric constant, dthe thickness of the insulator layer per volt of forming voltage andV_(F) the forming voltage.

The sintering of ultrafine primary and/or secondary structures creates avery large active capacitor surface area, but also forms closed poreswhose surface is inactive. The closed pores therefore reduce thevolume-based capacitance of the capacitors produced from the powders. Inthe case of use of secondary structures without closed pores, owing tothe higher volume-based capacitance, higher sintering temperatures canbe used in the production of the anode bodies without loss ofcapacitance, which in turn leads to an enhancement of the sinter necksand to better wire connection compared to the use of conventionalpowders. Better wire attachment and thicker sinter necks results in amore stable anode body and a better leakage current, ESR and surgeperformance of the capacitor.

It is therefore desirable to minimize the number and the volume ofclosed pores in the capacitor.

One measure of the open pore level of a capacitor anode and of thesecondary structures for use for capacitor production (agglomeratepowder) is the skeletal density thereof, which is defined as the ratioof the mass of the sinter body to the sum of volume of the solidscontent and volume of the closed pores. The skeletal density of theanode structures is measured by means of mercury intrusion porosimetry,also known as mercury porosimetry. The customary sintering processes toobtain capacitor anodes achieve skeletal densities of 80 to 88% of thetheoretical solid material density.

Processes for influencing the pore structure of capacitor anodes ofniobium or tantalum to obtain broad or bimodal pore size distributionshave already become known, in which so-called pore formers are usedduring the sintering step. EP 1291100 A1, WO 2006/057455 describe poreformers used which are organic substances which decompose or evaporatein the course of heating to the sintering temperature, or metals ormetal oxides or metal hydrides removable from the sintered structure byacid leaching after the sintering step. DE 19855998 A1 describes gaseouspore formers, by means of which adhesively bound highly porousagglomerates are obtained, which essentially maintain their porosity inthe course of sintering.

In these processes, the pore formers are used at relatively late processstages, in which sintered agglomerates with closed pores are alreadypresent, such that there is no effective prevention of the formation ofclosed pores.

When organic pore formers are used, the contamination of the capacitoranode body with carbon is moreover disadvantageous. When metals or metalcompounds are used, in addition to possible contamination, aconsiderable level of effort is required to remove pore formers from thesintered structures.

SUMMARY

An aspect of the present invention is to provide capacitor agglomeratepowders which enable the production of anode bodies with high skeletaldensity.

An alternative aspect of the present invention is to provide anodes forsolid electrolytic capacitors which have a high skeletal density andhence a high volume efficiency (capacitance/volume, CV/cm³).

A further alternative aspect of the present invention is to provideanode bodies which, after further processing to the capacitor, have animproved wire tensile strength, leakage current, ESR and/or surgeperformance.

In an embodiment, the present invention provides at least one of a valvemetal sintered capacitor anode body and a suboxide valve metal sinteredcapacitor anode body with a particle density of >88% of a theoreticaldensity.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described in greater detail below on the basisof embodiments and of the drawings in which:

FIG. 1 shows a typical diagram of the dependence of density andcompression pressure of a niobium suboxide sample.

DETAILED DESCRIPTION

The present invention provides valve metal and/or valve metal suboxideanode bodies, for example, niobium, tantalum and niobium suboxide anodebodies, such as niobium suboxide anode bodies of the formula NbO_(x)where 0.7<x<1.3, for example, where 0.8<x<1.1, with a skeletal densityof more than 88% of the theoretical density, for example, of more than90%, or more than 92%, of the theoretical density. According to thepresent invention, skeletal densities of up to 94% and more of thetheoretical density of the (compact) anode material are achievable. Inthe inventive anode bodies, the cumulated volume of the closed pores isless than 12%, for example, less than 10%, or, for example, less than8%, of the volume of the (compact) anode material.

Valve metals in the context of the present invention are understood tomean the metals from the group of niobium, tantalum and titanium.

The inventive agglomerate powders can, for example, consist of sinteredprimary particles with a mean cross-sectional dimension determined fromelectron micrographs of 0.1 to 2 μm, and an agglomerate size accordingto ASTM B 822 (“Mastersizer”, Daxad 11 wetting agent) of D10 from 3 to50 μm, D50 from 20 to 200 μm and D90 from 30 to 400 μm. The agglomeratepowder particles may have any desired forms, such as spheres, deformedspheres, fibres, chips, irregular morphology, etc., for example,spherical agglomerate powder particles, all forms described having a lowvolume of closed pores. The agglomerate powders have a good flowability(according to Hall, ASTM B 213) of less than 60 sec/25 g. The bulkdensity (according to Scott, ASTM B 329) in the case of niobium suboxideand niobium metal powders may advantageously be between 0.7 and 1.3g/cm³, and in the case of tantalum metal powders between 1.0 and 2.5g/cm³. The specific surface area (“BET”, ASTM D 3663) may advantageouslybe between 0.5 and 20 m²/g. The inventive agglomerate powders can, forexample, have a porosity determined by mercury intrusion (open pores) of50 to 70% by volume, more than 90% of the pore volume being formed bypores of diameter 0.1 to 5 μm.

The content of impurities, excluding conventional dopants such asnitrogen, phosphorus and/or vanadium, should be as low as possible. Thepowders can, for example, have contents of Fe, Cr, Ni, Cu, alkali metalsof less than 20 ppm, and of fluoride and chloride of less than 50 ppmeach. The carbon content can, for example, be less than 40 ppm. Anadvantageous nitrogen content can, for example, be 10 to 6000 ppm.Phosphorus contents in the inventive niobium suboxide powders aregenerally not detrimental. In niobium and tantalum metal powders,phosphorus of up to 500 ppm can be used to lower the sintering activityduring the generation of the secondary structures and the anodestructure. Optionally, before the sintering of the anode structure, thepowder can be treated with phosphoric acid, ammonium hydrogenphosphateor ammonium phosphate. Further, but less critical impurities of Al, B,Ca, Mn and Ti are, for example, less than 10 ppm, with Si below 20 ppm.

In an embodiment of the present invention, the inventive agglomeratepowder can, for example, have an increased densification coefficient αand an increased sliding coefficient η compared to prior art powders,which lead to better pressability of the powders. The product of BETsurface area in m²/g and sliding coefficient in the case of theinventive niobium suboxide powders can, for example, be 0.33 to 0.75,such as 0.45 to 0.58, in the case of the inventive tantalum powders 0.62to 0.95, for example, 0.65 to 0.86, and in the case of the inventiveniobium powders 0.38 to 0.8, for example, 0.42 to 0.6. The densificationcoefficient of the inventive agglomerate powders can, for example, begreater than 0.07 for niobium suboxide powder and greater than 0.08 forniobium and tantalum powder.

The present invention also provides niobium suboxide agglomerate powdersfrom which, after pressing to a press density of 2.8 g/cm³ and sinteringat a temperature of ≧1340° C., for example, of greater than 1400° C.,for 20 minutes, anode bodies are producible with a skeletal density ofmore than 88%, for example, more than 90%, or more than 92%.

The present invention further provides tantalum agglomerate powders fromwhich, after pressing to a press density of greater than 5 g/cm³ andsintering at a temperature of ≧1250° C. for 20 minutes, anode bodies areproducible with a skeletal density of more than 88%, for example, morethan 90%, or more than 92%.

The present invention also provides niobium agglomerate powders fromwhich, after pressing to a press density of 3.14 g/cm³ and sintering ata temperature of ≧1165° C., for example, ≧1180° C., for 20 minutes,anode bodies are producible with a skeletal density of more than 88%.

The present invention also provides a process for producing valve metaland/or valve metal suboxide agglomerate powders, which is characterizedin that precursor particles of the agglomerate powders are mixed with afine pore former, pore-rich, adhesively bounded agglomerates of theprecursor particles are obtained by densifying the mixture andevaporating or decomposing the pore former, the adhesively boundedagglomerates are subjected to a thermal treatment at a temperature andfor a duration sufficient for the formation of sinter bridges, and theat least partly sintered agglomerates are processed further in a mannerknown per se to valve metal and/or valve metal oxide agglomeratepowders.

The mixture can be densified dry by compacting the mixture underpressure, or wet by slurrying the mixture, for example, in water,densifying the slurry by means of ultrasound, pouring off thesupernatant liquid and drying.

In an embodiment of the present invention, tantalum, niobium and/orniobium suboxide agglomerates can be prepared having the formula NbO_(x)where 0.7<x<1.3, for example, 0.8<x<1.1.

The precursor particles for use in accordance with the present inventioncan, for example, be primary particles, or secondary particles formedonly from a few primary particles, of valve metals, such as niobiumand/or tantalum, and/or oxides thereof, such as pentoxides of niobiumand/or tantalum, with mean primary particle sizes less than 1 μm, forexample, less than 0.5 μm, or less than 0.3 μm, in the direction of thesmallest dimension. The particles may have any desired shape. Theprecursor particles can, for example, have a specific surface area ofmore than 80 m²/g, such as more than 100 m²/g.

The precursor particles used can, for example, be hydroxides or hydratedpentoxides, as obtained in the precipitation from aqueous niobiumfluoride and/or tantalum fluoride solutions with ammonia, which stillhave a sufficient water content of 25 to 35% by weight and a specificsurface area of more than 180 (in the case of Nb) or 100 m²/g (in thecase of Ta).

Pore formers can, for example, be ammonium salts such as halides,carbonates or oxalates. Examples include ammonium chloride and/orammonium oxalate.

The pore formers can, for example, be used with a mean particle size of0.5 to 20 μm, for example, 1.0 to 10 μm, or 1.5 to 5 μm, in an amount of10 to 90% by volume, for example, 15 to 60% by volume, 20 to 50% byvolume, or 30 to 45% by volume, based on the volume of the precursorparticles.

In the case of wet densification, the precursor particles can, forexample, be slurried with water. Other readily evaporable organicliquids with good wetting properties such as methanol, alcohols, ketonesand/or esters and mixtures thereof with water are likewise suitable.

With the slurrying of the precursor particles, the fine pore former ismixed intensively. Subsequently, the mixture is densified by shaking,for example, by means of ultrasound. Any supernatant liquid is removed,so as to form a moist cake.

The moist cake consisting of a mixture of precursor particles and poreformer particles is subsequently dried by gentle heating to atemperature of up to 150° C. in a transport gas stream, and the poreformer is removed completely from the cake by slow further heating to350 to 600° C.

Alternatively, the precursor particles comprising the fine pore former,after intensive dry mixing, can be densified at a pressure of 30 to 100bar, and then the pore former can be removed correspondingly by heating.

The dry cake consisting of adhesively bound precursor particles is,optionally after crushing and sieving, heated to a temperaturesufficient to form sinter bridges, so as to form a sintered open-poreprecursor agglomerate powder with high pore volume, which is essentiallyfree of closed pores.

The sintered precursor agglomerate powder is processed further in amanner known per se, as described below, to give the valve metal and/orvalve metal suboxide agglomerate powder.

The present invention further provides a process for producing valvemetal and/or valve metal oxide agglomerate powders, which ischaracterized in that precursor particles of the agglomerate powders areslurried in hydrogen peroxide or carbon dioxide-containing water, thewater is removed by drying to release oxygen gas or carbon dioxide, soas to obtain pore-rich, adhesively bounded agglomerates of the precursorparticles, the adhesively bounded agglomerates are subjected to athermal treatment at a temperature and for a duration sufficient for theformation of sinter bridges, and the at least partly sinteredagglomerates are processed further in a manner known per se to valvemetal and/or valve metal oxide agglomerate powders

During the drying of the slurry, water is withdrawn therefrom, while thehydrogen peroxide is decomposed to release oxygen gas or the solubilitylimit of the carbon dioxide in the remaining water is exceeded. The fineprecursor particles in the slurry act as bubble nuclei for the gasreleased. As long as sufficient moisture is still present, the bubblescannot escape from the slurry or agglomerate to large bubbles, so as toform an open-pore cake with large pore volume. The size of the poresformed by the bubbles and the pore volume of the cake can be controlledvia the amount of initially dissolved carbon dioxide or hydrogenperoxide.

In the case of use of carbon dioxide as the pore former, the slurry canalso be produced by dispersing the precursor particles in water under acarbon dioxide atmosphere or by stirring the hydroxides or hydratedpentoxides, as obtained in the precipitation from aqueous niobiumfluoride and/or tantalum fluoride solutions with ammonia, which stillhave a sufficient water content of 25 to 35% by weight and a specificsurface area of more than 100 m²/g, under a carbon dioxide atmosphere,optionally under pressure.

To completely remove the water, the dry cake obtained is heated to atemperature of 100 to 500° C.

The dried cake consisting of adhesively bound precursor particles is,optionally after crushing and sieving, heated to a temperaturesufficient to form sinter bridges, so as to form a sintered open-poreprecursor agglomerate powder which is essentially free of closed pores.

If niobium and/or tantalum metal powder are used as precursor powders,the sintered precursor agglomerate powders obtained therefrom aredeoxidized by mixing with magnesium turnings and heating in oxygen-freeatmosphere or under high vacuum, and then milled to the desiredagglomerate size.

Optionally, in a manner known per se, doping with nitrogen and/orphosphorus and/or vanadium can be effected by impregnating withsolutions of nitrogen- and/or phosphorus- or vanadium-containingcompounds before the deoxidation.

If pentoxides are used as precursor powders, they are reduced in amanner known per se according to WO 00/67936, in the case of niobiumpentoxide, for example, by first by heating in a hydrogenous atmosphereto the dioxide, with gaseous magnesium to the metal and optionallydoped.

To prepare NbO_(x) powders with the abovementioned definition of x, thestarting material is the abovementioned pentoxide precursor agglomeratepowder. Optionally, after hydrogen reduction to the dioxide, saidpentoxide precursor agglomerate powder is mixed intimately with astoichiometric amount of correspondingly finely divided niobium metalpowder and heated in a hydrogenous atmosphere, such that there isexchange of oxygen between the oxide and the metal. The finely dividedniobium metal powder used can, for example, be a niobium metal precursoragglomerate powder obtained in accordance with the present invention.

In a further process, the pentoxide precursor agglomerate powders,optionally after hydrogen reduction together with the niobium metalpowder, can again be mixed with pore formers, densified, removing thepore former, optionally sieved, and the adhesively bound powder mixtureagglomerate heated in hydrogen atmosphere so that there is exchange ofoxygen between the oxide and the metal.

The inventive niobium suboxide, niobium metal and tantalum metal powdersare suitable for the production of solid electrolytic capacitors withspecific capacitances of 20 000 to 300 000 μFV/g and very low residualleakage (also named as leakage currents) currents of less than 1 nA/μFV,for example, less than 0.2 nA/μFV, by customary processes.

To produce the anode bodies, the powder and a niobium or tantalum wireis placed into the mould and is pressed in the presence of binders andlubricants up to a pressed density of 2.3 to 3.5 g/cm³ in the case ofniobium or niobium suboxide powder or 4.5 to 7 g/cm³ in the case oftantalum powder to give green bodies, the green bodies being obtainedwith very favourable compressive strength. The pressed bodies containingthe contact wire can then, for example, be sintered in a niobium ortantalum boat at 1000 to 1500° C. for a sintering time of 10 to 25minutes under high vacuum at 10⁻⁸ bar. The sintering temperature andsintering time are, for example, selected such that the capacitorsurface area which can be calculated later from the capacitance of thecapacitor still has 65 to 45% of the specific surface area measured onthe powder.

The present invention further provides capacitors comprising a valvemetal and/or valve metal suboxide sintered capacitor anode body. Theinventive capacitors can be used in different electrical devices.

EXAMPLES Production of the Precursor Particles

V1: 75 l/h of aqueous H₂NbF₇ solution with a concentration of 81 g/l ofNb and 75 l/h of 9% aqueous NH₃ solution were added continuously to aninitial charge of 100 l of deionized water over 15 hours, such that thepH was 7.6±0.4. The temperature of the solution was kept at 63° C. Theresulting suspension was filtered through a pressure suction filter, andwashed with 3% aqueous NH₃ solution and then with deionized water. Theresulting moist niobium(V) hydroxide was dried at 100° C. in a dryingcabinet for 24 hours. The resulting niobium(V) hydroxide had a specificsurface area of 201 m²/g and spherical morphology.

V2: 40 parts by volume of deionized water were added with stirring to100 parts by volume of niobium(V) ethoxide solution. The precipitatedniobium(V) hydroxide (niobic acid) was filtered off by means of asuction filter and washed with deionized water. Subsequently, theniobium(V) hydroxide was dried at 100° C. for 17 hours. The powder had aspecific surface area of 130 g/m² and irregular morphology.

V3: The precursor particles V1 were calcined under air at 500° C. for 4hours and then milled in a jet mill to D90<10 μm (Mastersizer withoutultrasound treatment). Nb₂O₅ with a specific surface area of 89 m²/g wasobtained.

V4: 75 l/h of an aqueous H₂TaF₇ solution with a concentration of 155.7g/l of Ta and 75 l/h of a 9% by weight aqueous NH₃ solution wereconveyed continuously into an initial charge of 100 l of deionized waterover 30 hours, in the course of which the pH was kept at 7.6±0.4 and thetemperature of the solution was kept at 69° C. After removal byfiltration, washing with 3% NH₃ solution and deionized water, and dryingat 100° C. over 24 hours, tantalum(V) hydroxide with a specific surfacearea of 106 m²/g and spherical morphology was obtained.

V5: The precursor particles V4 were calcined under air at 500° C. for 2hours and milled in a jet mill to D90<10 μm. A Ta₂O₅ powder with aspecific surface area of 83 m²/g was obtained.

Preparation of Sintered Agglomerate Pentoxide Powders (P1-P14)

To prepare the sintered pentoxide powders P1 to P14, the precursorsspecified in Table 1 column 1 were used.

The precursors were mixed with the amount specified in Table 1 column 3(% by weight based on the pentoxide) of a pore former specified incolumn 2 with a mean particle size of 1.5 μm either in aqueoussuspension (“wet” in column 4) or dry (“dry” in column 4). In the caseof wet mixing, the suspension of the settled solids mixtures wasdensified by means of ultrasound, supernatant water was poured off anddrying was effected at 110° C. over 15 hours. In the case of dry mixing,the dry powder mixture was densified with a hydraulic laboratory press(die diameter 5 cm, fill height 3 cm) at 75 bar over 1 minute.

TABLE 1 Column 3 4 6 7 Pentoxide 1 2 Amount % Amount % 5 Heat SinteringNo. Precursor Pore former by wt. by wt. Densification treatment ° C., h° C., h P1 V1 (NH₄)₂(C₂O₄) 30 22.8 wet 600, 3 1300, 5 P2 V1 — — wet 600,3 1300, 5 P3 V2 (NH₄)₂(C₂O₄) 30 23.5 wet 600, 3 1300, 5 P4 V2 — — wet600, 3 1300, 5 P5 V2 (NH₄)₂(C₂O₄) 40 28.9 wet 600, 3 1300, 5 P6 V2 — —wet 600, 3 1300, 5 P7 V3 NH₄Cl 30 21.8 dry 600, 2 1150, 5 P8 V3 — — dry600, 2 1150, 5 P9 V4 (NH₄)₂(C₂O₄) 20 38.1 wet 600, 3 1600, 5 P10 V4 — —wet 600, 3 1600, 5 P11 V4 NH₄Cl 20 36.8 dry 600, 2 1450, 5 P12 V4 — —dry 600, 2 1450, 5 P13 V5 NH₄Cl 20 34.6 dry 600, 2 1600, 5 P14 V5 — —dry 600, 2 1600, 5

The dried (adhesively bound agglomerates) or pressed (pressings) powdermixtures were subsequently, in order to decompose the pore former,heated to the temperature specified in column 5 of Table 1 for the timewhich is likewise specified there. This was followed by sintering at thetemperature and for the duration specified in column 6 under air.

The sintered agglomerates were crushed with a jaw crusher, milled a ballmill and sieved to <300 μm.

Preparation of Metal Powders (M1 to M14)

The pentoxide powders P1 to P14 were converted to metal powders M1 toM14, in the case of niobium pentoxide after reduction to niobium dioxideby means of hydrogen at 1300° C., by reduction with magnesium vapour at900° C. under argon (as the transport gas) over 6 hours, cooling,passivating, sieving below 300 μm, removing the magnesium oxide by meansof 8% sulphuric acid and washing to neutrality with deionized water.Table 2 reports the BET surface areas, the D50 values according toMastersizer (without ultrasound treatment) and the sums of the impuritycontents of iron, chromium and nickel, of fluorine and chlorine, and ofsodium and potassium.

TABLE 2 Powder M1 M2 M3 M4 M5 M6 M7 M8 M9 M10 M11 M12 M13 M14 BET, m²/g6.5 6.7 5.7 5.6 5.5 5.4 8.1 7.8 4.8 4.4 6.2 5.9 5.3 5.4 Fe + Cr + Ni, 89 5 8 10 11 8 6 9 7 10 5 4 7 ppm F + Cl, ppm <5 6 <5 6 5 <5 9 <5 <5 <5 9<5 8 <5 Na + K, ppm <3 <3 <3 4 <3 <3 <3 <3 <3 3 <3 <3 <3 <3 D50, μm 4139 162 159 169 172 123 110 37 32 68 73 143 154

Preparation of Niobium Suboxide Powders (S1 to S10)

To prepare the niobium suboxide powders, in each case, the niobiumpentoxide specified in column 1 of Table 3 was mixed dry with 3 timesthe stoichiometric amount of the niobium metal specified in column 2 ofTable 3 and the pore former specified in column 3 (20% by weight basedon metal and pentoxide), densified at 75 bar and heat treated at 600° C.over 3 hours to remove the pore former.

The dry cake was then heated to the reaction temperature specified inTable 3 in a hydrogen atmosphere for 4 hours, cooled, passivated andsieved to <300 μm. Table 6 reports the BET surface areas, the D50 valuesaccording to Mastersizer (without ultrasound treatment) and the sums ofthe impurity contents of iron, chromium and nickel, of fluorine andchlorine, and of sodium and potassium. Additionally reported are thedensification coefficient α and the sliding coefficient η, as definedbelow, and the products of sliding coefficient η and the BET surfacearea.

TABLE 3 Column 4 1 2 3 Reaction Suboxide Pentoxide Metal Pore formertemperature ° C. S1 P3 M3 NH₄Cl 1050 S2 P3 M3 NH₄Cl 1250 S3 P3 M3 NH₄Cl1400 S4 P3 M3 NH₄Cl 1500 S5 P3 M3 — 1400 S6 P4 M4 NH₄Cl 1400 S7 P4 M4 —1400 S8 P3 M2 NH₄Cl 1400 S9 P1 M1 NH₄Cl 1400 S10 P2 M2 — 1400

Preparation of Deoxidized Metal Agglomerate Powders (D1 to D14).

For deoxidation, powders M1 to M8 and M10 to M14 were each mixed with 8%by weight (niobium metal powder) or 5% by weight (tantalum metal powder)of magnesium turnings and an amount of an NH₄H₂PO₄ solution sufficientfor doping with 100 ppm of phosphorus, and heated to 850° C. for 2 hoursunder argon, cooled and passivated, and sieved to <300 μm. Two samplesof powder M9 were deoxidized at temperatures of 850 and 750° C. and arereferred to hereinafter as M9a and M9b. Tables 4 and 5 report the BETsurface areas, the D50 values according to Mastersizer (withoutultrasound treatment) and the sums of the impurity contents of iron,chromium and nickel, of fluorine and chlorine, and of sodium andpotassium. Additionally reported are the densification coefficient α andthe sliding coefficient η, as defined below, and the products of slidingcoefficient η and the BET surface area.

Production of Anode Bodies

The deoxidized metal powders D1 to D14 and niobium suboxide powders S1to S8 and a tantalum wire of thickness 0.3 mm were placed into the pressmould of diameter 3.6 mm and a length of 3.6 mm and pressed to a densityin g/cm³ specified in Tables 4, 5 and 6, and were then sintered underhigh vacuum for 20 minutes at the temperature in ° C. specified in thetables.

TABLE 4 Example 1 2 3 4 5 6 7 8 9 10 Deoxidized D1 D2 D3 D4 D5 D6 D7 D8niobium metal powder Precursor powder M1 M2 M3 M4 M5 M6 M7 M8 Fe + Cr +Ni, ppm 7 7 4 9 9 12 7 7 F + Cl, ppm <5 <5 5 <5 <5 <5 9 <5 Na + K, ppm<3 <3 <3 3 <3 <3 <3 <3 D50, μm 47 43 179 163 172 181 109 122 D90, μm 7175 280 299 281 301 245 251 Densification 0.09 0.05 0.09 0.06 0.11 0.040.11 0.05 coefficient α Sliding coefficient η 0.33 0.19 0.39 0.28 0.410.25 0.11 0.08 BET, m²/g 1.65 1.71 1.15 1.09 1.11 1.08 4.8 4.40 η × BET0.54 0.32 0.45 0.31 0.46 0.27 0.53 0.35 Anodes: Press density, g/cm³3.14 3.14 3.14 3.14 3.14 3.14 3.14 3.14 3.14 3.14 Sinter temp., ° C.1165 1165 1165 1200 1165 1200 1165 1165 1165 1165 Skeletal density, % 9187 92 91 87 86 93 87 93 87

TABLE 5 Example 11 12 13 14 15 16 17 18 19 20 Deoxidized D9a D9b D10 D11D12 D13 D14 Ta metal powder Precursor Ta powder M9a M9b M10 M11 M12 M13M14 Fe + Cr + Ni, ppm 9 9 6 9 7 5 8 F + Cl, ppm <5 <5 <5 8 <5 7 <5 Na +K, ppm <3 <3 <3 <3 <3 <3 <3 D50, μm 36 35 33 73 67 162 159 D90, μm 63 5855 152 159 258 241 Densification 0.10 0.09 0.06 0.09 0.06 0.09 0.05coefficient α Sliding coefficient η 0.31 0.17 0.24 0.26 0.19 0.29 0.2BET, m²/g 2.52 4.11 2.47 3.1 3.07 2.91 2.84 η × BET 0.78 0.70 0.59 0.810.58 0.84 0.57 Anodes: Press density, g/cm³ 5.0 5.0 5.0 5.75 5.0 5.755.0 5.0 5.75 5.75 Sinter temp., ° C. 1250 1250 1250 1250 1250 1250 12501250 1250 1250 Skeletal density, % 92 91 85 82 93 92 84 82 92 85

TABLE 6 Example 21 22 23 24 25 26 27 28 29 30 31 32 33 34 Suboxide S1 S2S3 S3 S4 S5 S5 S6 S6 S7 S7 S8 S9 S10 powder Fe + Cr + 6 7 7 6 <5 <5 <5 76 <5 Ni, ppm F + Cl, ppm 6 <5 7 6 <5 <5 <5 7 6 <5 Na + K, ppm <3 3 <3 <3<3 3 <3 <3 <3 <3 D50, μm 151 168 181 195 171 189 178 101 59 51 D90, μm261 273 269 298 281 279 271 210 94 82 Densification 0.12 0.12 0.13 0.120.11 0.09 0.06 0.09 0.09 0.05 coefficient α Sliding 0.2 0.27 0.29 0.40.25 0.23 0.16 0.25 0.28 0.15 coefficient η BET m²/g 2.5 2 1.8 1.3 1.841.75 η × BET 0.50 0.54 0.52 0.52 0.29 0.26 Anodes: Press density, 2.82.8 2.8 2.8 2.8 2.8 2.8 2.8 2.8 2.8 2.8 2.8 2.8 2.8 g/cm³ Sinter temp.,1340 1340 1340 1460 1340 1340 1460 1340 1460 1340 1460 1340 1340 1340 °C. Skeletal 96 94 94 93 94 93 91 90 89 87 86 92 94 85 density, %

The densification coefficient α (compactibility α) and the slidingcoefficient η were determined in a powder testing centre model PTC-03DTfrom KZK Powder Tech Corp., Chantilly, Va., USA.

The densification coefficient was determined by introducing powders(without binder or lubricant) into a die of diameter D=12.7 mm, andpressing with a plunger to a height of H12.694 mm, the pressure p_(c) onthe plunger being measured during the pressing. A typical diagram whichshows the dependence of density and compression pressure of a niobiumsuboxide sample is reproduced in FIG. 1.

The densification coefficient α is determined by the following equation:

|log|log ρ_(ra)∥=α log ((p _(r) +p ₀)/p ₀)+|log|log ρ_(rp)∥,

where ρ_(rp) is the tap density of the powder, ρ_(ra) is the meandensity of the pressed body after compression under the pressure p_(r,),and p₀ is the gravitational pressure on the powder (weight of the powderdivided by the cross-sectional area of the die).

To determine the sliding coefficient, the pressure p_(d) at the bottomof the die was additionally measured on attainment of a pressed densityof 4.8 g/cm³ in the case of tantalum, 3.14 g/cm³ in the case of niobiumand 2.8 g/cm³ in the case of niobium suboxide. The sliding coefficient ηwas determined by the following equation:

p_(d)/p_(c)=η^(SH/4F)

where S is the cross-sectional circumference πD and F is thecross-sectional area πD²/4.

The present invention is not limited to embodiments described herein;reference should be had to the appended claims.

1-25. (canceled)
 26. At least one of a valve metal sintered capacitoranode body and a suboxide valve metal sintered capacitor anode body witha particle density of >88% of a theoretical density.
 27. The at leastone of a valve metal sintered capacitor anode body and a suboxide valvemetal sintered capacitor anode body as recited in claim 26, wherein theparticle density is >90% of the theoretical density.
 28. The at leastone of a valve metal sintered capacitor anode body and a suboxide valvemetal sintered capacitor anode body as recited in claim 26, wherein acomposition of the at least one of a valve metal sintered capacitoranode body and a suboxide valve metal sintered capacitor anode body isNbO_(x), wherein 0.7<x<1.3.
 29. The at least one of a valve metalsintered capacitor anode body and a suboxide valve metal sinteredcapacitor anode body as recited in claim 26, wherein the at least one ofa valve metal sintered capacitor anode body and a suboxide valve metalsintered capacitor anode body consists of tantalum or niobium.
 30. Aniobium suboxide agglomerate powder having a product of a BET surfacearea in m²/g and a sliding coefficient of η of 0.33 to 0.75.
 31. Aniobium suboxide agglomerate powder having a densificationcoefficient >0.07.
 32. Method of using the niobium suboxide agglomeratepowder as recited in claim 30 to produce an anode body with a particledensity of >88%, the method comprising: providing the niobium suboxideagglomerate powder as recited in claim 30; pressing the niobium suboxideagglomerate powder to a press density of 2.8 g/cm³; and sintering theniobium suboxide agglomerate powder to a temperature of >1340° C. so asto provide the anode body.
 33. A tantalum agglomerate powder having aproduct of a BET surface area in m²/g and a sliding coefficient η of0.62 to 0.95.
 34. A tantalum agglomerate powder having a densificationcoefficient of >0.08.
 35. Method of using the tantalum agglomeratepowder as recited in claim 33 to produce an anode body with a particledensity of >88%, the method comprising: providing the tantalumagglomerate powder as recited in claim 33; pressing the tantalumagglomerate powder to a press density of 5.0 g/cm³; and sintering thetantalum agglomerate powder to a temperature of >1250° C. so as toprovide the anode body.
 36. A niobium agglomerate powder having aproduct of a BET surface area in m²/g and a sliding coefficient η of0.38 to 0.8.
 37. A niobium agglomerate powder having a densificationcoefficient of >0.08.
 38. Method of using the niobium agglomerate powderas recited in claim 36 to produce an anode body with a particle densityof >88%, the method comprising: providing the niobium agglomerate powderas recited in claim 36; pressing the niobium agglomerate powder to apress density of 3.14 g/cm³; and sintering the niobium agglomeratepowder to a temperature of >1165° C. so as to provide the anode body.39. Method for producing at least one of a valve metal agglomeratepowder and a valve metal oxide agglomerate powder for producing asintered capacitor anode body, the method comprising: either A) mixingprecursor particles of the at least one of a valve metal agglomeratepowder and a valve metal oxide agglomerate powder with fine pore formersto obtain a mixture; compacting the mixture so as to provide pore-rich,adhesively bound agglomerates of the precursor particles; and thermallyremoving the fine pore formers; or B) slurrying precursor particles ofthe at least one of a valve metal agglomerate powder and a valve metaloxide agglomerate powder with hydrogen peroxide or carbon dioxide so;and removing water via drying so as to release oxygen or carbon dioxideso as to provide pore-rich, adhesively bound agglomerates of theprecursor particles; and then thermally-treating the adhesively boundagglomerates of the precursor particles at a temperature and for aduration so as to form sinter bridges; and further processing the atleast partially sintered adhesively bound agglomerates of the precursorparticles so as to provide the at least one of a valve metal agglomeratepowder and a valve metal oxide agglomerate powder.
 40. The method asrecited in claim 39, wherein the fine pore formers are ammonium saltswith an evaporation, a sublimation or a decomposition temperature of<600° C.
 41. The method as recited in claim 40, wherein the fine poreformer is at least one of a finely divided ammonium chloride and anammonium oxalate.
 42. The method as recited in claim 39, wherein thefine pore former is used in an amount of 10 to 90% by volume based onthe volume of the precursor particles.
 43. The method as recited inclaim 39, wherein the precursor particles have a specific surface areaof >80 m²/g
 44. A capacitor anode produced by: providing at least one ofa valve metal sintered capacitor anode body and a suboxide valve metalsintered capacitor anode body having a particle density of >88% of atheoretical density; and forming the capacitor anode from the at leastone of a valve metal sintered capacitor anode body and a suboxide valvemetal sintered capacitor anode body.
 45. A capacitor comprising thecapacitor anode as recited in claim
 44. 46. A capacitor comprising atleast one of a valve metal sintered capacitor anode body and a suboxidevalve metal sintered capacitor anode body having a particle densityof >88% of a theoretical density.
 47. Method of using the capacitor asrecited in claim 46 in an electrical device, the method comprising:providing the capacitor as recited in claim 46; and arranging thecapacitor in the electrical device.
 48. A capacitor anode, the capacitoranode produced by pressing and sintering at least one of a niobiumsuboxide agglomerate powder having a product of a BET surface area inm²/g and a sliding coefficient of η of 0.33 to 0.75, a tantalumagglomerate powder having a product of a BET surface area in m²/g and asliding coefficient η of 0.62 to 0.95 and a niobium agglomerate powderhaving a product of a BET surface area in m²/g and a sliding coefficientη of 0.38 to 0.8.
 49. A capacitor comprising the capacitor anode asrecited in claim
 48. 50. Method of using the capacitor as recited inclaim 49 in an electrical device, the method comprising: providing thecapacitor as recited in claim 49; and arranging the capacitor in anelectrical device.